Clarify why we save ziplist elements in revserse order.

Also get rid of variables that are now kinda redundant, since the
dictionary iterator was removed.

This is related to PR #3949.

1 files changed, 13 insertions, 7 deletions

diff --git a/src/rdb.c b/src/rdb.c
index c6a88081b..1a5a7b2c5 100644
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -709,17 +709,23 @@ ssize_t rdbSaveObject(rio *rdb, robj *o) {
             if ((n = rdbSaveLen(rdb,zsl->length)) == -1) return -1;
             nwritten += n;
 
+            /* We save the skiplist elements from the greatest to the smallest
+             * (that's trivial since the elements are already ordered in the
+             * skiplist): this improves the load process, since the next loaded
+             * element will always be the smaller, so adding to the skiplist
+             * will always immediately stop at the head, making the insertion
+             * O(1) instead of O(log(N)). */
             zskiplistNode *zn = zsl->tail;
             while (zn != NULL) {
-                sds ele = zn->ele;
-                double *score = &zn->score;
-
-                if ((n = rdbSaveRawString(rdb,(unsigned char*)ele,sdslen(ele)))
-                    == -1) return -1;
+                if ((n = rdbSaveRawString(rdb,
+                    (unsigned char*)zn->ele,sdslen(zn->ele))) == -1)
+                {
+                    return -1;
+                }
                 nwritten += n;
-                if ((n = rdbSaveBinaryDoubleValue(rdb,*score)) == -1) return -1;
+                if ((n = rdbSaveBinaryDoubleValue(rdb,zn->score)) == -1)
+                    return -1;
                 nwritten += n;
-
                 zn = zn->backward;
             }
         } else {